Immonoassays, in which antibodies are used in various formats to detect analytes, play an important role in the fields of clinical diagnostics, environmental analysis and basic biological research. Many rapid methods for detecting protein analytes, bacterial analytes with high selectivity and sensitivity have been developed in the past years. These include radio-activity based immunoassay, chemiluminescence based immunoassay, magnetic based assay, fluorescence or colormetric based immunoassay. Many are commercially available, evaluated and validated under stringent requirement testing programs. Some rapid test systems incorporate more than one immunology-based technology into the test system to improve specificity and/or sensitivity. Immunology-based rapid assays already in existence can be further modified or incorporated into other systems to improve their performance, which obviates the need to create entirely new detection systems.
Array based immunoassay technologies for multianalytes detection has exploded since the introduction of DNA microarrary technology in the early 90s. The technology that produces high-density arrays formed by spatially addressable synthesis of bioactive probes on a 2-dimensional solid support has greatly enhanced and simplified the process of biological research and development. The key to current microarray technology is deposition of a bioactive agent at a single spot on a microchip in a “spatially addressable” manner. An alternative approach to the spatially addressable method is the concept of using fluorescent dye-incorporated polymeric particles to produce biological multiplexed arrays. U.S. Pat. No. 5,981,180 discloses a method of using color coded particles in conjunction with flow cytometry to perform multiplexed biological assay. Microspheres conjugated with DNA or monoclonal antibody probes on their surfaces were dyed internally with various ratios of two distinct fluorescence dyes. Hundreds of “spectrally addressed” microspheres were allowed to react with a biological sample and the “liquid array” was analyzed by passing a single microsphere through a flow cytometry cell to decode sample information. U.S. Pat. No. 6,023,540 discloses the use of fiber-optic bundles with pre-etched microwells at distal ends to assemble dye loaded microspheres. The surface of each spectrally addressed microsphere was attached with a unique bioactive agent and thousands of microspheres carrying different bioactive probes combined to form “particles array” on pre-etched microwells of fiber optical bundles. More recently, a novel optically encoded microsphere approach was accomplished by using different sized zinc sulfide-capped cadmium selenide nanocrystals incorporated into microspheres (Nature Biotech. 19, 631–635, (2001)). Given the narrow band width demonstrated by these nanocrystals, this approach significantly expands the spectral barcoding capacity in microspheres.
Even though the “spectrally addressed microsphere” approach does provide an advantage in terms of its simplicity over the old fashioned “spatially addressable” approach in microarray making, there was still a need in the art to make the manufacture of biological microarrays less difficult and less expensive.
U.S. Ser. No. 09/942,241 provides a microarray that is less costly and easier to prepare than those previously disclosed because the support need not be modified. Nevertheless, the microspheres remain immobilized on the substrate. U.S. Ser. No. 09/942,241 provides a microarray comprising: a substrate coated with a composition comprising microspheres dispersed in a fluid containing a gelling agent or a precursor to a gelling agent, wherein the microspheres are immobilized at random positions on the substrate. The substrate is free of receptors designed to physically or chemically interact with the microspheres. That invention utilizes a unique coating composition and technology to prepare a microarray on a substrate that need not be pre-etched with microwells or pre-marked in any way with sites to attract the microspheres, as disclosed in the art.